1. Field
This disclosure relates to digital image watermarking, more particularly to a method for inserting a watermark into blocks of an image.
2. Background
Traditionally, a watermark is an image formed on the surface of paper. When held up to a light, the watermark image can be seen in the paper. One application of such marks is to verify the authenticity of documents or other printed images. Currencies, money orders, legal documents, among many other examples, are typically printed on paper stock having the appropriate watermark. When these printed images are received, the recipient can hold the paper up to the light and verify its authenticity. Using specially ‘coded’ paper places an additional layer of security in the process of creating printed images.
With the advent of computer networks, including the Internet, many images are copied from providing sites and passed around without ever being printed. It becomes problematic for image providers to track proprietary images. A copy of a digital image will typically be the exact same as the original image, unless there was some corruption in the data. Providers of these images have no way to detect if this person obtained this image in violation of intellectual property laws, or if the copy obtained belongs to the image provider. In addition, recipients of a digital image may want to ensure that the digital image received is from a particular source and is not a hoax or fabricated image. The watermark can be extracted that provides this information.
In response to this problem, a new industry of digital watermarking has arisen. A digital watermark is typically some sort of identifying image that is ‘hidden’ in the original image data. Digital images can have from hundreds to millions bits of data. A digital watermark is buried somewhere in the image data in such a manner that it can be extracted by those who know how and where it was buried, yet remain undetected by those that do not know the necessary information. In this way, illegal copying of images can be detected upon analysis of the image, and the individual performing the copying cannot detect and eliminate the watermark. Similarly, verification of authentic images can be performed to ensure that images received are from a particular source.
However, inserting watermarks into digital images have two problems. While the ability to bury the data in complicated methods allows for higher security, too much complication can increase processing time before the digital image data is resolved into an image. Alternatively, if the watermark is too simple, it may be removed by a simple filtering operation, rendering the watermark useless. Further, watermarks can degrade the quality of the image, as manipulation of the image data may result in objectionable artifacts.